The skies are full of birds today, but birds didn’t always exist. Scientists have wondered at how flight developed among feathered dinosaurs ever since the first fossilized specimens were discovered. Now, a team of researchers from Tsinghua University in Beijing has used a dinosaur robot and an ostrich backpack to show that dinosaurs might have been flapping their wings before they even had them.

In the past, we all envisioned dinosaurs as scaly lizard-like creatures, but it has become increasingly clear many of them sported feathers. Perhaps the most famous feathered dinosaur is Archaeopteryx, the first fossil of which was discovered in 1861. Simply knowing that elements of avian flight evolved in the Jurassic period doesn’t tell you how it happened. There are numerous theories, but evidence currently points to a transition from running to flapping flight without an intermediate gliding stage. The research led by Tsinghua’s Jing-Shan Zhao focused on a dinosaur called Caudipteryx to probe that transition.

The Caudipteryx is considered the most primitive non-flying winged dinosaur, making it an ideal subject for studying the anatomy of pre-flight. Caudipteryx weighed about 11 pounds (five kilograms) and could run around 26 feet per second. You can think of it as a fast, prehistoric turkey. The team used a mathematical model known as modal effective mass theory to predict the mechanics of running for Caudipteryx. Using that data, the team built a robot version of Caudipteryx to see how it might have run.

The math and the robot agree that Caudipteryx’s proto-wings most likely flapped as a consequence of running. So, passive flapping may predate avian flight, offering a potential evolutionary path that doesn’t include gliding. They also fitted a juvenile ostrich with a backpack with similar proto-wings. They confirmed that passive flapping motions occurred as the ostrich ran.

This is an interesting perspective on the evolution of flight, but it does include a lot of guesswork. For example, we don’t know enough about Caudipteryx’s musculature to create a faithful robotic representation. The aerodynamics of the proto-wings are also impossible to replicate from fossils. Flight may also have evolved at different times and in different ways, and we don’t know which dinosaur species were the precursors to the birds of today. It’s a problem that requires more research, but hopefully, that research includes dino robots.